 Other than getting enough sleep, what can we do to improve the glumphatic clearance of waste from our brains? The provision of a running wheel, so mice could voluntarily exercise, has been shown to improve glumphatic clearance in aging mice, which was accompanied by a reduced build-up of amyloid deposits and improved cognition. Sleeping position may also make a difference. Studies on rats show that their natural sleeping position curled up on their sides allows for better glumphatic transport than sleeping on their backs or stomachs. People also tend to spend most of their time sleeping on their side, particularly their right side versus left, compared to their backs or stomachs. This may maximize blood outflow from the brain. When we sleep on our right side, our right internal jugular vein, the main blood vessel in our neck draining blood from the head, is wide open. And our left jugular is partially collapsed, and vice versa. Since most people have a dominant right jugular vein, sleeping on their right side might maximize brain drainage. Does it matter? Well, people with neurodegenerative disease, mostly mild cognitive and permanent, Alzheimer's disease, tend to sleep more on their backs than those with normal cognition. About 72% spend at least two hours a night on their backs, compared to 37% of those with healthier brains, raising the intriguing possibility that head position during sleep could influence the clearing of neurotoxic proteins from the brain. In crib death, sudden infant death syndrome, sleeping position can be a lifesaver, leading to slogans like back to sleep, or more morbidly, face up to wake up. It's premature for an adult jingle, maybe on your flank to not draw a blank. The characteristic position of poor sleepers is on their back though, so maybe it's the poor sleeping rather than the position per se that leads to cognitive decline, or the causality could be reversed with dementia-deteriorating good sleep habits. Even if sleeping position did matter, it may take a night in a sleep lab to track your movements. It turns out self-reported sleep positions are often false. Should brain benefits to side sleeping ever be established, you can train yourself with so-called positional therapies, such as the tennis ball technique, which involves wearing a shirt to bed backwards with a ball stuffed in the chest pocket. The uncertainties don't end with sleeping position. The glimphatic mechanism itself was rapidly embraced in scientific circles and the popular press. However, it's been controversial. It wasn't until 2019 that the first evidence was published that the glimphatic system discovered in rodents even existed in human brains. Even the relationship between sleep and Alzheimer's disease is perhaps best summed up in a recent neurology review entitled It's Complicated. Yes, those getting less than 7 hours of sleep may have higher rates of Alzheimer's, but those getting more than 8 are at higher risk, too. If anything, population studies show that longer sleep durations, more than 8 or 9 hours, are more strongly linked to Alzheimer's disease and dementia in general than sleeping less than 5 or 6 hours. The association between dementia and long sleep duration could be reverse causation, where prodromal changes in the brain years before Alzheimer's is diagnosed causes prolonged sleep. Long sleep duration may also just be a confounding factor, a marker of some underlying health problem that's the real culprit. For example, oversleeping may be a sign of depression, which itself is an established risk factor for dementia. But there is a plausible biological mechanism for how extended sleep duration could increase dementia risk directly. Longer sleep duration, typically defined as sleeping more than 8 hours a night, is associated with signs of systemic inflammation, elevated levels of C-reactive protein and into lukin 6. And both of those inflammatory markers, in turn, are associated with an increase in dementia risk. So much more needs to be teased out about the role of the glymphatic system before we make conscious efforts to tweak it.